Spark plug



June 3, 1930. G. H. E BERTHOLD SPARK PLUG Filed Feb. 26, 1927 ATTORNEYPatented June 3, 1930 UNITED STATES PATENT, OFFICE GEORGE E. E.IBERTHOLD, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO THE RAJAH GOMIANY, OFBLOOMFIELD, NEW JERSEY, A CORPORATION OF NEW JERSEY SPARK PLUGApplication filed February 26, 1927. Serial No. 171,188.

cylinder of an internal combustion motor.

Due partly to the extreme differences in temperature to which theseveral parts of a spark plug are subjected when in operation, andpartly to the difierence of the coefficients ofexpansion of the severalmaterials used, great difliculty has been experienced in the manufactureof a spark plug in which certain of the parts would stand up undercontinued hard use. A further ditliculty experienced has been failure toobtain tight joints between the several parts which results, especiallywhen used in the modern high compression type motor, in loss ofcompression of the combustion charge, and a consequent loss of power ofthe motor.

One of the disadvantages in a spark plug for use in a high compressionengine is the difliculty of keeping'tight the joint between the core orporcelain of the plug and the central electrode. This electrode usuallyruns through an elongated hole and is cemented in place. Thelongitudinal expansion of the electrode, aggravated by its radialexpansion also, serves to break and disintegrate the cement which worksits way out through the lower end of the core. It is well known that thegases under high compression work their way through minute openings. Theplug therefore leaks and the engine loses some-of its compression. Oneof my objects is to provide a construction for adequately scaling in thecentral electrode which shall not be open to these objections.

. With the above and other objects in view, reference is had to theaccompanying drawings in which the'figure is a longitudinal sectionalview of a spark plug illustrating the improvements of the presentinvention.

In the drawings, 10 designates the shell which may be of any preferredtype and 12 designates the shell electrode. The shell is externallythreaded as at 14 in the usual mannerto provide for its attachment inoperating position, and is further provided with an internally threadedrecess 16' for the reception of a threaded bushing or collar 18 employedto retain the core 20 in position in the shell. A gasket 22 is employedand placed under compression by the bushlng or collar 18 in the usualmanner to provide a gas-tight joint between the shell 10 and the core20.

The core 20 has a passage extending entirely therethrough, and thispassage is preferably formed with an enlarged internally screw threadedportion providing an internally screw threaded recess 24 and aconstricted portion forming an electrode passage 26. The bottom of therecess 24 is preferably formed with a seat 28.

The center electrode 30 is preferably carried by a plug 32 which isexternally threaded for engagement with the interior thread of therecess 24, and when said plug 32 is secured in position, the electrode30 projects through the electrode passage at the lower .end of the core20 and into proximity with the shell electrode 12 but slightlyspacedtherefrom.

Surrounding the center electrode 30, and adapted to be received upon theseat 28 of the recess 24, there is a washer 34. This washer 34 closelyfits the electrode, whereby it prevents the cement from, being carriedbelow it, and is preferably of a pliable nature, and when forced inwardconforms to the seat and exterior of the electrode and forms anadditional sealing means.

To provide an effective seal for the center electrode 30 and the plug32, cement is employed, and said cement is interposed'beftween theinnerend of the plug 32 and the washer 34 as designated at 36. This cement isof sucha nature that when the plug 32' is screwed into the recess 24 toposition the electrode 30 in, the core 20, the cement willbe placedundercompression against the washer 34 and the seat 28, andwill alsobeforced into intimate contactwith the electrodeand certain of "thethreadsiof the recess andthe seals the central electrode 30 and the plug32 and prevents the leakage of gas there- .plug. l The setting of thecement completely I I to receive an electric conductor terminal, anduponlts under face, the head 40 is formed or provided with an annularflange 42 providing a recess 44 for the reception of a suitable packing46. This packing 46 is placed under compression upon screwing the plug82 into the recess 24 of the core 20, and also serves in combinationwith the cement 36, as a sealing means for preventing the escape of gasaround the center electrode 30.

The central electrode 30 has at least a loose fit 1n the passage 26 andpreferably is sufliclently smaller in diameter than the passage so thatit will not contact therewith. It is sealed at its upper end by thecement and washer which are obviously held under high compresslon by thescrew plug 32. The electrode may therefore expand and contract withoutdanger of rupturing the gas seal.

From the foregoing, it will be apparent that the present inventionprovides a new and improved spark plug in which the several parts are soconstructed and assembled as to withstand without rupture, the varioustemperatures to which they are subjected in use. Furthermore, a sparkplug constructed in accordance with the present invention is thoroughlygas-tight, thus insuring greater efficiency in motors of the'highcompression While in the present instance but one form of the inventionhas been illustrated, it is to be understood that the invention is notlimited to the form shown, but may be practiced in various other formswithin thescope of the appended claims.

What is claimed is:

1. A spark plug comprising an insulating core having a longitudinal boretherethrough,

a central electrode mounted in said bore being 5 of a size and shaperelative to the bore such that that portion of the electrode which iswithin the part of the insulating core exposed in use to the heat ofburning gases will be free to expand and contract radially andlongitudinally without interference from said core,

said core being formed with a recess into which the bore openssubstantially above that part of the core which is exposed to theextreme temperature changes, a washer in the bottom of said recessfitting tightly about the electrode and into the bottom of the recessand a narrow band of a sealing material within said recess compressedinto intimate sealing contact with the electrode and with theinsulating'core and which serves to press said washer into a closersealing contact with the electrode and the core.

2. A spark plug comprising an insulating core having a longitudinal boretherethrough, a central electrode mounted in said bore being exposure tothe free to expand and contract radially and longitudinally withoutinterference from said core, said core being formed with a recess intowhich the bore opens substantially above that part of the core which isexposed to the extreme temperature changes, a washer of a materialadapted to resist crumbling when subjected alternately to abrasive andtensile stress at high temperatures fitting tightly about the electrodeand into the bottom of the recess, and a narrow band of a refractoryhardened plastic cement compressed in said recess into intimate sealingcontact with the electrode and with the insulatin core and which servesto press said was or into a closer sealing contact with the electrodeand the core.

3. A spark plug as defined in claim 1 in which the bore through the coreis not sufliciently larger than the electrode to permit free access ofburning or combustible gases therein.

4. A spark plug comprising an insulating core having a longitudinal boretherethrough, a central electrode mounted in said bore being of a sizeand shape relative to the bore such that that portion of the electrodewhich 1s within the part of the insulating core exposed in use to theheat of burning gases will be free to expand and contract radially andlongitudinally without interference from said core, said core beingformed with a recess into which the bore opens substantially above thatpart of the core which is exposed to the extreme temperature changes, awasher of a material adapted to resist crumbling when subjectedalternately to abrasive and tensile stress at high temperatures, fittlngtightly about the electrode and into the bottom of the recess and anarrow band of a refractory hardened plastic cement compressed in saidrecess into intimate sealing contact with the electrode and .;with theinsulating core and which serves to press said washer into a closersealing contact with the electrode and the core, the band by which theelectrode is cemented into the corebeing within that portion of the corewhich is cooled by atmosphere, and the space between the core and theelectrode at normal temperatures of continuous operation being notsubstantially in excess of that required to permit radial expansion ofthe electrode at maximum temperatures which may be expected underconditions of operation.

Signed at New York, N. Y., this 24th day of February, 1927.

GEORGE H. E. BERTHOLD.

of a size and shape relative to the bore such

